Artificially sweetened beverages like Diet Coke are often considered healthier alternatives, but the debate over their impact on obesity persists. Previous research has predominantly relied on observational data or randomized controlled trials (RCTs), which may not accurately capture the causal relationship between Diet Coke consumption and obesity. This study uses causal inference methods, employing data from the National Health and Nutrition Examination Survey (NHANES) to examine this relationship across diverse demographics. Instead of relying on RCT data, we constructed a causal graph and applied the back-door criterion with its adjustment formula to estimate the RCT distributions. We then calculated the counterfactual quantity, the Probability of Necessity and Sufficiency (PNS), using both NHANES data and estimated RCT data. We propose that PNS is the essential metric for assessing the impact of Diet Coke on obesity. Our results indicate that between 20% to 50% of individuals, especially those with poor dietary habits, are more likely to gain weight from Diet Coke. Conversely, in groups like young females with healthier diets, only a small proportion experience weight gain due to Diet Coke. These findings highlight the influence of individual lifestyle and potential hormonal factors on the varied effects of Diet Coke, providing a new framework for understanding its nutritional impacts on health.

翻译：人工甜味剂饮料（如零度可乐）通常被视为更健康的替代品，但关于其对肥胖影响的争论持续存在。以往研究主要依赖观察性数据或随机对照试验（RCT），这可能无法准确捕捉零度可乐消费与肥胖之间的因果关系。本研究采用因果推断方法，利用美国国家健康与营养调查（NHANES）数据，探索这一关系在不同人口群体中的表现。我们并未依赖RCT数据，而是构建因果图，应用后门准则及其调整公式来估计RCT分布。随后，基于NHANES数据和估计的RCT数据，计算反事实量——必要性与充分性概率（PNS）。我们认为PNS是评估零度可乐对肥胖影响的关键指标。结果显示，20%至50%的个体（尤其是饮食不良者）更易因饮用零度可乐而体重增加；相反，在年轻女性等饮食更健康的群体中，仅少数人因零度可乐导致体重上升。这些发现凸显了个人生活方式与潜在激素因素对零度可乐差异化效应的作用，为理解其营养健康影响提供了新框架。